Hair straightener



FIG. 1 is a perspective view of a hair straightener showing a new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a left side view thereof.

The broken lines are shown for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a hair straightener, as shown and described. 